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Let’s compare Palaeocene Ignacius to recent Dactylopsila – again.

Tuesday, September 29, 2026 6:49

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Ignacius is a plesidapiform from the Palaeocene of Wyoming.
Most likely arboreal, Ignacius (Fig 1, Matthew and Granger 1921) nests as a basalmost taxon in the Placentalia 3 clade in the large reptile tree (LRT, 2340 taxa). That makes it basal to rodents (including rabbits and sirenians via beavers) and Jurassic multituberculates.

So… Ignacius is an ancient placental 3 mammal.

Current workers consider plesiadapiformes (which lack canines) ancestral to primates (which have canines). The LRT does not recover that interrelationship.

Figure 1. Dactylopsia and Ignacius skeletons, not to scale.

Wikipedia reports,
“Ignacius, along with the other plesiadapiforms, possess large, procumbent lower incisors convergent with those found in rodents, however, unlike rodents, the incisors of plesiadapiforms were not continuously growing.”

Figure 2. Recent arboreal marsupials, Petaurus and Dactylopsila, compared to Palaeocene (and probably way earlier) Ignacius. They are closely related in the LRT. Here is where Ignacius loses teeth to create a rodent-like diastema in the anterior maxilla. The premaxillary teeth were taphonomically lost.

Dactylopsila is a striped possum native to New Guinea and Australia
This squirrel-like marsupial (Fig 3) with a 26cm body length and 32cm prehensile tail is closely related to the sugar glider, Petaurus (Fig 2). Dactylopsila eats wood-boring insect larvae, as in another related taxon in the LRT, the extant aye-aye, Daubentonia (Fig 4), but that’s another story. The female has two teats in her pouch and can give birth to up to two young.

Figure 1. The extant striped opossum Dactylopsila in vivo. — Figure 3. The extant striped opossum Dactylopsila in vivo.

According to Google AI
“[These] two completely separate mammal genera [Dactylopsila and Ignacius] are frequently compared in evolutionary biology due to their similar feeding habits.”

Figure 2. Skeleton of Daubentonia (aye-aye). Like other plesiadapids, it convergences with the lemuroid primates. — Figure 4. Skeleton of Daubentonia (aye-aye). Like other plesiadapids, it is not related to primates in the LRT, but precedes multituberculates and rodents.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

References
wiki/Ignacius
wiki/Dactylopsila

That earlier blogpost from 2024
Today’s update corrects earlier errors on the interpretation of the skull of Ignacius.

Source: https://pterosaurheresies.wordpress.com/2026/09/29/lets-compare-palaeocene-ignacius-to-recent-dactylopsila-again/

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